1. Field of the Invention
This invention relates to a method and apparatus for economically and reliably anchoring a conventional bridge plug within the production casing of a completed oil or gas well.
2. Prior Art
A conventional means and a well-known method for plugging a completed oil or gas well is best described when referring to FIG. 1 of the drawings. As will be recognized by those skilled in the art, the subsurface formation 2 of a site upon which a well is to be completed often has formation characteristics (such as fluid saturation and the distribution of permeability and porosity) that are indicative of commercial accumulations of trapped hydrocarbons at multiple pay zones. A hole 1 of suitable dimension is drilled into the subsurface formation 2 at the well-site, and a pipe 4 is extended therethrough. By way of example, the pipe 4 is a production casing having a five inch outside diameter. Casing 4 is usually fabricated from a suitable high strength material such as steel, or the like. The casing 4 generally comprises pipe sections of approximately 30 feet in length that are connected end-to-end with one another. An area 6 lying between the subsurface formation 2 of the well-site and the casing 4 is typically constructed and filled with a cement, in order to provide the well with sufficient zonal isolation. The cement selected to fill area 6 has suitable temperature and pressure resistant characteristics. By way of example, one type of cement that is available for utilization in the completion of an oil or gas well is that commonly known as American Petroleum Institute (API) Class E cement.
A hollow, cylindrical production packer 8 is run down the hole 1 and secured to the sides of casing 4 at a suitable location above the lower-most production zone, wherein high concentrations of hydrocarbons have been detected. By way of example, the lower-most production zone may occur at a depth of approximately 10,000-15,000 feet. The packer 8 is generally fabricated from a two foot long section of high strength material, such as iron, or the like. As will be known to those skilled in the art, the packer 8 has associated therewith a plurality of slips 10, or biting edges. When packer 8 is lowered to a desired position in hole 1 above a production zone, an explosive charge is detonated, whereby to cause the slips 10 to penetrate and bite the walls of casing 4 and, thereby, secure the position of packer 8 thereat. A run of tubing 12 is inserted into the hole 1, so that the downside end thereof is received by packer 8. Hence, the packer 8 acts to retain tubing 12 above the anticipated production zone, so as to prevent a blow-out of tubing 12 when receiving hydrocarbons that are released at high pressures.
The conventional oil or gas well is completed when a plurality of perforations 14 are formed to permit the interface of tubing 12 with the (lower-most) production zone, wherein trapped deposits of hydrocarbons lay. As will be understood by those skilled in the art, the perforations are created by either of well-known bullets or jet shots by conventional perforating guns at high pressure. The perforations 14 extend through the walls of casing 4 and the cemented area 6, so as to communicate with the production zone.
As will be recognized by those skilled in the art, after the completion of the oil or gas well, the subsurface formation 2 may be fractured (in the event of a low permeability formation) according to conventional techniques, by applying to the production zone thereof a fracturing solution (i.e. gel) under high pressure. The fracturing solution is conveyed to the production zone via tube 12 and each of the plurality of perforations 14. Upon termination of the fracture treatment, suitable access to the trapped hydrocarbons can be achieved, so that accumulated oil or gas deposits may be extracted from the hole 1 through perforations 14 and tubing 12.
Upon depletion of the deposited hydrocarbons in the (lower-most) production zone, it is usually desirable to tap deposits that are trapped in other production zones located at lesser depths below the surface of the well-head. However, and prior to the time when a new production zone may be treated, the depleted, lower-most production zone and the new, untapped production zone must be isolated from one another. As will be appreciated by those skilled in the art, one conventional technique by which to plug back the perforations 14 associated with the lower-most production zone and thereby block communication with well hole 1 contemplates the utilization of a well-known workover rig (not shown). The workover rig is positioned over the hole 1 and is adapted to release the tubing 12 from the packer 8, so that tubing 12 can be withdrawn from the interior of hole 1. However, in order to remove packer 8 so as to squeeze cement into perforations 14, the packer 8 must be destroyed. The destruction of packer 8 is typically accomplished by means of drilling thereover with a suitable milling bit. A suitable plug 15 is then inserted into hole 1 by a conventional squeeze process, whereby to plug the perforations of the lower-most production zone. By way of example, the aforementioned plug 15 is deposited at the bottom of hole 1 by pumping cement, under pressure, thereto. After sufficient time for the cement plug to cure, a new packer and tubing are fixedly inserted within hole 1 above the new production zone. Access to the new production zone may thereupon be obtained to recomplete the well, as was previously disclosed.
However, the conventional procedure for withdrawing hydrocarbons from multiple production zones lying at various subsurface depths is highly disadvantageous. That is, very expensive operating costs are attributable to the utilization of a workover rig (to seal up a lower-most production zone and to recomplete the well), the intricate tooling commonly associated therewith, and the need for trained operators. Furthermore, work over of the well will accelerate wear and promote an early replacement of the related tooling. Accordingly, the high operating costs associated with a workover rig relative to the expected yield often contributes to the capping of those wells having only moderate production capabilities. The lack of production zones of sufficiently large area may make the completion of an oil or gas well commercially unfeasible, because of the expense of recompleting from one zone to another. Hence, vast reserves of greatly needed hydrocarbons may go substantially untapped.
Moreover, utilization of a workover rig and the conventional technique for recompleting an oil or gas well is relatively time consuming. That is, the time which has heretofore been expended to remove the packer and tubing so as to permit a cement plug 15 to be inserted and cured each time that a new production zone is to be completed and stimulated undesirably reduces the efficiency by which needed hydrocarbons can be obtained.
What is more, and as previously disclosed, each time that the hydrocarbon deposits are depleted from a lower-most production zone, the packer is first destroyed, so that a squeeze can be performed on the production zone being abandoned. The destructive process required to gain access to new production zones further increases both the risk of damage to production casing 4 and the cost associated with the development of oil and gas reserves.
What is still more, the cement plug 15 that is usually deposited at the bottom of the oil or gas well to plug back an old production zone is both expensive and, at times, unreliable. That is, increasing formation pressures commonly associated with production intervals at large subsurface depths are known to cause fissures within the conventional cement plug. Such fissures may undesirably result in communication between an old, depleted production zone and a new, untapped zone located thereabove.
Therefore, as will be readily appreciated by those skilled in the art, prior art apparatus and procedures by which to complete and recomplete an oil or gas well in order to successively tap a plurality of production zones is highly disadvantageous, because of the high costs, time consumption, and unreliability generally associated therewith.